Re: [PATCH] mm: Fix potential NULL pointer dereference

[Libin <huawei.libin@huawei.com>]

On 2013/7/25 22:01, Michal Hocko wrote:
> On Wed 24-07-13 11:48:19, Libin wrote:
>> find_vma may return NULL, thus check the return
>> value to avoid NULL pointer dereference.
> 
> Please add a note that the check matters only because
> khugepaged_alloc_page drops mmap_sem.
> 

Thanks for your suggestion. I will add the information
and post the patch soon.

Regards,
Libin.

>> Signed-off-by: Libin <huawei.libin@huawei.com>
> 
> Other than that
> Reviewed-by: Michal Hocko <mhocko@suse.cz>
> 
> + I guess this is worth backporting to the stable trees. This goes back
> to when khugepaged was introduced AFAICS.
> 
>> ---
>>  mm/huge_memory.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 243e710..d4423f4 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -2294,6 +2294,8 @@ static void collapse_huge_page(struct mm_struct *mm,
>>  		goto out;
>>  
>>  	vma = find_vma(mm, address);
>> +	if (!vma)
>> +		goto out;
>>  	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
>>  	hend = vma->vm_end & HPAGE_PMD_MASK;
>>  	if (address < hstart || address + HPAGE_PMD_SIZE > hend)
>> -- 
>> 1.8.2.1
>>
>>
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